In installations for treating containers such as bottles, it may be necessary to modify the spacing pitch of successive containers during the passage from one treatment station to a subsequent treatment station. This may be the case, for example, for feeding a treatment station with containers or bottles having to undergo a plasma treatment which makes it possible to achieve the formation of an internal coating in the containers or bottles. It is, therefore, necessary to provide a system for conveying discrete entities allowing the discrete entities to be transferred from the feed device to the treatment station whilst increasing the pitch or the spacing between two successive or immediately adjacent entities so that the two immediately adjacent entities are fed to the treatment station at the pitch corresponding to the spacing pitch of two immediately adjacent treatment stations.
It is known to use a system with a variable pitch feed screw, capable of pivoting on itself and allowing the pitch to be increased between two successively fed containers.
An example of such an embodiment of a variable pitch feed screw is shown according to a side view in FIG. 1, FIGS. 2 and 3 respectively illustrating said variable pitch feed screw according to a side schematic view and a transverse schematic sectional view.
Means for feeding discrete entities, of the container or bottle 2 type, are provided upstream of the variable pitch feed screw 1, each container body 2 being capable of being engaged in the region of the upstream end la of the screw 1 in a groove or slot 3 formed on the circumference of the screw 1, the pitch of the slot 3 increasing between the upstream end 1a and the downstream end 1b of the feed screw 1. The bottom of each container 2 thus bears against an endless belt conveyor 4. In order to maintain the bottle or container 2 in the slot 3 and in the position bearing against the endless belt conveyor 4, a plurality of fixed guides 5, 6, 7, preferably in the form of rails, is provided. Two fixed guides 5, 6 are advantageously provided and shaped so that the side of the body of the bottle or the container 2 which opposes the side of the container or the bottle 2 housed in the slot 3 of the feed screw 1, is capable of sliding on these two fixed guides 5, 6. Additionally, a third fixed guide 7 is also provided, capable of being engaged beneath an annular projection or flange 8 either of the bottle or of the container 2.
If it is desired to increase the pitch between two containers fed successively on a variable pitch screw, it is necessary, therefore, to increase the length of the feed screw as the pitch between the articles is always substantially the same at the inlet of the screw due to the fact that the containers are against one another. From now on, only the diameter of the container influences this inlet pitch whilst at the outlet of the screw, the pitch depends on what is desired to be achieved. In other words, the pitch of the screw at the outlet dictates the length thereof. As a result, the container is accelerated from its inlet velocity to its outlet velocity, producing forces on the container which may be squashed and marked. Thus, to avoid this occurrence, the length of the transition from one pitch to another is exploited and so is the total length of the screw. However, this length poses the problem of its flexibility, vibrations, and of the difficulty of handling a screw of great length when changing the size of container. As a result, the use of screws of great length proves to be unacceptable in current practice.
Moreover, in order to press down the containers or bottles properly into the slot 3 of the feed screw 1, the endless belt conveyor 4 runs at a velocity greater than the velocity of the bottle in the feed screw 1. In this manner, the container 2 is held upright in the slot 3 and is stabilized. Nevertheless, the greater the pitch at the outlet of the screw, the greater the velocity of the conveyor 4 has to be.
It should also be pointed out that the transport of containers by means of a variable pitch feed screw is liable to leave scratch marks on the body of the container thus transported, this risk being all the greater, the greater the pitch and thus the greater the angle.
Moreover, as a result of the size of such an endless screw, it would also be difficult to incorporate such a screw in an installation where it is desired to limit the overall spatial requirement.
It is also necessary to consider that a feed screw of great length is heavy and not easy to handle. It would thus be difficult to replace such a feed screw of great length easily and by using just one person.
Moreover, it should also be noted that a screw of great length is more difficult to control.
For certain applications, for example for loading containers in stations for depositing a barrier coating by means of plasma excited by electromagnetic waves, a much greater extension of the pitch is required, which is able to reach, for example, 72π.
All the above considerations tend to limit the implementation of feed screw devices with variations in pitch not exceeding a certain limit. To sum up, the variation of pitch between containers for feeding machines such as filling machines or labelling machines is limited to values in the order of 25π to 30π.
The object of the invention is, therefore, to propose means (a method and device) making it possible to increase the pitch between entities fed in succession whilst limiting the total spatial requirement of such a system and facilitating the operations of replacement and maintenance.